1. Technical Field
This invention relates generally to sound engineering, and more specifically to digital signal processing methods and apparatuses for calculating and creating an audio waveform, which, when played through headphones, speakers, or another playback device, emulates at least one sound emanating from at least one spatial coordinate in four-dimensional space
2. Background Art
Sounds emanate from various points in four-dimensional space. Humans hearing these sounds may employ a variety of aural cues to determine the spatial point from which the sounds originate. For example, the human brain quickly and effectively processes sound localization cues such as inter-aural time delays (i.e., the delay in time between a sound impacting each eardrum), sound pressure level differences between a listener's ears, phase shifts in the perception of a sound impacting the left and right ears, and so on to accurately identify the sound's origination point. Generally, “sound localization cues” refers to time and/or level differences between a listener's ears, time and/or level differences in the sound waves, as well as spectral information for an audio waveform. (“Four-dimensional space,” as used herein, generally refers to a three-dimensional space across time, or a three-dimensional coordinate displacement as a function of time, and/or parametrically defined curves. A four-dimensional space is typically defined using a 4-space coordinate or position vector, for example {x, y, z, t} in a rectangular system, {r, θ, φ, t,} in a spherical system, and so on.)
The effectiveness of the human brain and auditory system in triangulating a sound's origin presents special challenges to audio engineers and others attempting to replicate and spatialize sound for playback across two or more speakers. Generally, past approaches have employed sophisticated pre- and post-processing of sounds, and may require specialized hardware such as decoder boards or logic. Good examples of these approaches include Dolby Labs' DOLBY Digital processing, DTS, Sony's SDDS format, and so forth. While these approaches have achieved some degree of success, they are cost- and labor-intensive. Further, playback of processed audio typically requires relatively expensive audio components. Additionally, these approaches may not be suited for all types of audio, or all audio applications.
Accordingly, a novel approach to audio spatialization is required, that places the listener in the center of a virtual sphere (or simulated virtual environment of any shape or size) of stationary and moving sound sources to provide a true-to-life sound experience from as few as two speakers or headphones.